


Xenobiology 101

by MarquessBrie



Category: Undertale (Video Game)
Genre: Breeding, F/M, Light Bondage, Mind/Mood Altering Substances, Non-Consensual, Oviposition, Pheromones, Pregnancy, Reader-Insert, Tentacles, Unplanned Pregnancy
Language: English
Status: Completed
Published: 2017-11-04
Updated: 2017-11-04
Packaged: 2019-01-29 06:00:28
Rating: Explicit
Warnings: Rape/Non-Con
Chapters: 1
Words: 1,498
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/12624756
Author URL: https://archiveofourown.org/users/MarquessBrie/pseuds/MarquessBrie
Summary: The monsters came out from under the mountain a few years ago, and since then Dr. Gaster had frequented your coffee shop. Things have been going strangely ever since. It got to the point that you had to call out sick today... Or was it yesterday?





	Xenobiology 101

**Author's Note:**

  * For [NihilismPastry](https://archiveofourown.org/users/NihilismPastry/gifts).



The sensation is a strange combination of fuzzy and frozen that you find affecting your head. Fragments of ideas hang suspended in your mind, refusing to coalesce into a coherent thought.

The wind howled outside the dark room. It was only a little cold, goosebumps dotting your flesh. You tried to wrap your arms around yourself, but couldn't seem to get them to move the way you wanted them to. 

It was actually pretty hard to move them at all. That… probably should have alarmed you. No matter how your muscles strained, you couldn't free yourself from the soft ooze holding your arms behind your head.

Something that _was_ readily apparent to your addled mind was how incredibly aroused you were. The feeling in your head felt a little familiar, a much stronger version of a feeling you remember… from work?

“Barrissta,” a strange, gutteral and hissing voice shattered your fragile train of thought. A smooth, sheet white face was in the doorway in front of you, framed by an amorphous black mass that shifted bonelessly as he moved. Lines broke the paleness going up and down from wide black sockets.

“You rressponded beautifully to the pherromonezz. It izz interressting how ssussceputible you arre to them…” A dark tendril caressed your body, from your neck down to your hip… that you were naked probably should have been alarming too, perhaps. You could only arch into the attention, illustrating his point quite nicely.

“Therre izz time forr notess laterr, though, my dearr,” he purred, smiling, crescent mouth full of sharp teeth. “Now you will sserrve me in anotherr capacity, barrissta.” He flowed up to you, more tendrils reaching for you, caressing your body. Two hands, as white as his face, gripped your waist, pulling you back towards him. The sensations were making you moan, heedless of any audience you might have.

His face lowered to your neck, and a long, slimy tongue slipped free of his fangs, sliding over you, lighting your nerves with bliss wherever that strange saliva touched.

“What musst it have been like forr you, I wonderr?” He whispered into your flesh. “I found you outsside my doorr in a hazze, turrembling with cold and durripping with dezzirre.” The buzzing, hissing drone of his voice pulled a scene into your mind. 

~*~

_Ever since the monsters had come out from under the mountain, your libido had gone through the roof. Professor Gaster had almost instantly secured a job at the local University, the one whose entrance was by the cafe you worked at._

_At first, the professor struck you as odd. His accent was thick, unlike any of the other monsters you had encountered, and he looked strange, slimy and sinuous aside from a bone white face and hands._

_He kind of grew on you, though. You started to find his rolled “r”s and pronounced lisp endearing. You also started to think of what that strange body was capable of in… other contexts._

_It got to the point that just the thought of him brought a blush to your face, and imagining those wet, muscular tentacles (they had to be tentacles, right? You'd never seen them apart from one another, but that made the most sense) slide over your body had become your favorite masturbatory aid._

_As the storm rolled in you started feeling strange. You felt hot, and fuzzy and sluggish. You couldn't be expected to work like this, so you called in._

_You tried to rest, tried to sleep it off, but the haze just grew. You needed help. You stumbled out of your apartment, and you weren't sure if you'd locked the door behind you. You were wearing nothing but a long night shirt, and it was snowing. You had to get to help. The snow felt good at first, but soon you were shivering._

_You came to a door._

_He would help._

~*~

He took pity on you, finally. Something thick and slimy slid against your lower lips, and you cried out when it made contact with your swollen clit.

“You will make a lovely hosst for my childrren, barrissta,” he crooned, pressing the dull tip into your entrance. It was wide, and quickly filled you entirely. Something kept toying with your nub, drawing panting moans from you. “You arre sso pliable alrready,” he was pressing against your cervix, and the pain of that bled into pleasure, pushing you further. “But you can melt morre.”

Tentacles coiled around every sensitive part of you. Your nipples, your neck, your sides, your thighs, rubbing and squeezing and slipping over you. The tendril playing with your clit became more insistent, motions harder, faster.

The orgasm was almost ripped from you, and you screamed with the pleasure of it. Even as it washed over you, as your inner walls clenched at the phallus inside you it thrust deeper, through the ring of your cervix and into your womb.

This seemed to be just what he was waiting for, a feral growl rumbling through him as your body clutched and squeezed at him. He began rocking his hips, starting slow. It was agonizing, and the excruciating pain began burning away the thick haze coating your mind.

Why were you so attracted to a monster? What had he said about pheromones earlier? He is really fucking you right now, and it really hurts!

His speed built, and your desperate squirming changed reasons. Before it became too much, though he groaned, thrusting as deeply as he could, spilling hot seed into you. 

Suddenly all the pain and discomfort melted into pleasure, and the pleasurable fog washed over you, swept you away again. He thrust a few more times, and the narcotic seed leaked around him, dripping down your thighs in thin rivulets, lines of ecstasy tracing where your mind drained out.

“Therre you arre, my ssweet,” he purred into your ear. “I hope you arre rready to be a motherr, barrissta!” 

He pulled his body back from you, affording you a clear view of exactly what was happening to your overstimulated body. That thick length piercing you corresponded to a white tentacle, stark against his obsidian body. From where the two met you could see a bulge forming, getting bigger and bigger before moving down the length until it was pressing against you. 

You wanted it. You desperately wanted that bulge inside you. It was the only thing you could comprehend right now. He rocked his hips back, and you whined as it left with him. His laugh rumbled through you both, amused yet hungry, and it melted into a moan as he pushed the bulge down his length to press at your lips again.

He thrust into you, and you saw sparks. The pleasure was incredible, feeling that bulge within your entrance, and he just kept going, kept fucking you, growling into your ear. It was pressing into your cervix now, and your breath was stuttering.

It thrust through, and you arched with your second orgasm of the night, howling with pleasure. He moaned with you as the bulge emerged out of the end of the tentacle, shifting around inside you as he continued to fuck you mercilessly.

Another bulge pressed at your entrance, and this one entered easier, but was quickly followed by a third. He'd lost all eloquence, rutting these orbs, these eggs?, into you, growling and moaning with some primal need.

And you wanted them.

Every egg he had to give you, you wanted all of them and more. They came so quickly that your orgasms began to merge together, your body trembling with overstimulation, awash with the sparking sensation of climax each time one made its way into your womb with his impassioned thrusts.

You weren't sure when this had stopped, but the monster had collapsed against you, apparently spent. He stroked your distended stomach with one hole-palmed hand.

“You did verry well, barrissta,” he purred, face nuzzling into your neck. “They will need to incubate forr a few dayzz. I will take carre of you in the meantime. I underrsstand humanss can become dehydrrated, let me burring you ssome waterr…” he pulled himself up off of you entirely, white tentacle nowhere to be seen in the mass of black, before slithering off.

The restraints seemed to have released you. You moved trembling hands to your belly, feeling how the eggs had changed its shape. They shifted inside you, subtly, but it was enough to wash your mind away with pleasure, to make you moan. Professor Gaster chuckled at that. He'd returned, and seemed to be holding a straw to your lips.

“The ssubsstancce my eggss are exxcurreated with sseemzz to rreact differrently with human chemissturry.” He noted. “I will like to ssee how theirr hatching affectss you azz well.” His free hand stroked your cheek, and you couldn't help but close your eyes into the caress.

Your head was still really fuzzy, but there was a strange sense of deep satisfaction there now, too.


End file.
